For what it's worth, that's a problem faced by many drugs with side effects, especially psychoactive ones. Sometimes active placebos are used, as in the magic m

For what it's worth, that's a problem faced by many drugs with side effects, especially psychoactive ones. Sometimes active placebos are used, as in the magic mushroom studies at Johns Hopkins (I believe they used a stimulant). But even people who've never used psychedelics can probably tell whether they've taken speed or hallucinogens. I didn't read the study in depth, but the problem you describe is widespread and well-known. Well-known doesn't mean solved, so perhaps you have a better solution? One option might come from clever experimental design, in which subjects do not know the hypothesis you wish to test. The problem is that this is often guessable - i.e. here subjects might not have known that AP was being tested, but they might have believed mental performance was, and if they thought they were in the treatment group they might have extra confidence, which could confound the results. That's hard to design around in practice, though.